CNN - John Allen Chau was an adventurer who hiked in North Cascades National Park in the Pacific Northwest, traveled to Israel and went on mission trips to South Africa. But he was always drawn to North Sentinel Island off the coast of India, and the people there.

The Sentinelese live in isolation on the remote island in the Andaman and Nicobar archipelago, protected by Indian law to maintain their way of life and protect them from modern illnesses because they lack immunity. Chau took a scouting trip to the Andaman islands several years ago and told people of his desire to return, said a friend, John Middleton Ramsey.

Chau's zeal to spread the Christian gospel took him back to the remote island, where he apparently was killed last week by tribespeople after trespassing, authorities said. Contact with the isolated tribe is prohibited. But those who knew the American missionary are calling him a martyr for the Christian faith.